1. Field of the Invention
The present disclosure is related to a rotating container. More particularly, the present disclosure is related to the braking of a tub or basket that is subject to a rotational speed.
2. Description of Related Art
Vertical axis washing machines, also known as top loading washing machines, represent a large portion of the overall washing machine consumer market in the United States. Horizontal axis washing machines represent a smaller segment of the United States market and abroad typically represent a larger portion of the overall washing machine consumer market.
Most vertical axis and horizontal washing machines include a spin cycle for removing water and/or detergents from the laundry using centrifugal force and spinning a wash load tub, also referred to as a laundry tub (“tub”) or basket. During a typical spin cycle, the motor, typically an induction motor, of the washing machine spins the tub at relatively high speed(s).
Historically induction motors used in washers have been single phase induction motors or PSC induction motors. More recently three-phase induction motors, have been used in some commercially available washers. The three-phase motors in washers for home use are typically powered by standard single phase AC household electric power. As part of a three-phase induction motor washing machine, a circuit associated with the motor converts the single phase AC household electric power to three phase power; the three phase power is better at motor starting and operates more efficiently than single phase power.
A simplified explanation of an induction motor, ignoring losses follows: The induction motor has a rotor with a short-circuited winding inside a stator with a rotating magnetic field. The flux from the rotating field induces a current flow in the rotor. The frequency of the current flowing is equal to the difference between the rotational speed of the stator field and the rotational speed of the rotor. This difference in speed, or frequency, of the stator magnetic field and the rotor magnetic field is known as the slip.
The rotor current causes a rotor magnetic field, which is spinning relative to the rotor at the slip frequency and relative to the stator field, at the same slip frequency. The interaction between rotor magnetic field and the stator magnetic field generates a torque in the rotor.
A wash load wash cycle has various modes such as fill, drain and spin, agitation, and spin. Braking can occur before, during or after various segments of the wash cycle. Braking can be dictated by wash cycle parameters and also by safety standards, such as UL safety standards. Typical intermittent wash load braking during the spin mode of the wash cycle is performed in accordance with UL safety standards. For example, if a lid, such as the lid of a vertical washing machine, is opened during the spin modes or cycle, the wash load brakes within a predetermined time limit, such as a 7 second stop-time that is a UL safety standard. Other safety standards and/or stop times may also be available for safety purposes during various modes of the wash cycle.
Some prior art washing machines or washers typically rely upon mechanical brakes such as brake pads or shoes to bring a rotating load, such as a washing machine tub, to zero speed or zero angular velocity in a clothes washer.
The use of brake pads or shoes to stop a washing machine tub is costly and also affects the life of the washing machine dependent upon use since each brake shoe or pad has a wear surface that is subject to wear and eventually, after a period of use, will fail due to wear. Hence there is a wide variation in life of a washer model configured with brake pads or shoes, depending upon subjective factors, i.e. the user or consumer's use of the washing machine including frequency of use and type of use. The type of use varies in the selection of cycle such as a gentle cycle or a heavy-duty cycle. The braking of spin associated with a gentle cycle likely causes less brake wear than the braking of spin associated with a heavy-duty cycle. There are also variations in braking dependent upon the load size or water level used. A large load may spin longer and at greater angular velocity than a small load; thus causing greater wear on the brake. A higher water level, using more water than a lower level, less full load, would also require additional spin for water removal and could cause greater wear on the brake.
Other prior art washing machines or washers use permanent magnet motors and control circuits to provide braking to the washer without using a brake pad or shoe applied to the washer tub to bring the rotating load to zero speed or zero angular velocity. Generally a permanent magnet motor operates like a generator when braking; typical excess electrical energy from the generator mode is either dissipated via a brake resistor or a power resistor controlled appropriately or it is sent out to the electrical system using, for example, the line synchronization technique.
Accordingly, there is a need for a washing machine that overcomes, alleviates, and/or mitigates one or more of the aforementioned and other deleterious effects of prior art washing machines.